The present invention relates to a squeegee for screen printing for printing paste such as cream solder or conductive paste on a substrate, a screen printing method, and a screen printing apparatus.
In an electronic component mounting process, screen printing is employed as a method of printing paste such as cream solder or conductive paste on a substrate. This method comprises a step of setting a mask plate having pattern holes opened according to the printing positions on a substrate, and a step of printing the paste on the substrate through pattern holes by supplying the paste on the mask plate and sliding a squeegee.
In this screen printing, as the squeegee moves above the mask plate in the horizontal direction, the paste is applied into the pattern holes, and this paste is printed on the substrate which is set underneath the mask plate. Such conventional printing method included a step of scraping and collecting the paste by a plate member inclined in the running direction, and a step of filling the pattern holes with the paste by moving the squeegee and pressing the paste against the mask plate.
To enhance the productivity, meanwhile, it is demanded to shorten the cycle time also in the electronic component mounting process. It, therefore, requires higher printing speed in the screen printing, that is, a higher sliding speed of the squeegee. However, by sliding a conventional squeegee at high speed, some of pattern holes may be left unfilled to cause printing failure.
It is hence an object of the invention to present a squeegee for screen printing and a screen printing method capable of filling the pattern holes favorable with the paste material even in high speed printing process and enhancing the productivity.
The squeegee of the invention is used in screen printing for printing the paste supplied on the mask plate on the substrate through the mask plate, by sliding above the mask plate having the pattern holes in the running direction. The squeegee comprises a contacting portion for contacting with the surface of the mask plate, a filling portion disposed at the running direction side of the contacting portion, and an agitating portion disposed at the running direction side of the filling portion, in which the agitating portion has a function of rotating the paste by sliding of the squeegee, the filling portion has a function of filling the pattern holes with the paste along with the sliding motion, and the paste applied in the pattern holes can be printed on the substrate.
The screen printing method of the invention for printing paste on a substrate comprises (a) a step of putting the substrate at the lower side of a mask plate having pattern holes, (b) a step of supplying paste on the mask plate, and (c) a step of sliding a squeegee in the running direction while contacting with the mask plate and scraping and collecting the paste, in which the step of sliding the squeegee includes (1) a step of sliding the squeegee for generating a rotary motion on the paste, (2) a step of filling the pattern holes with the rotating paste, and (3) a step of printing the paste applied in the pattern holes on the substrate.
The screen printing apparatus of the invention for printing paste on a substrate comprises a substrate positioning portion for mounting the substrate, a mask plate disposed above the substrate, and a squeegee slidable above the mask plate. The mask plate has pattern holes, the squeegee can slide above the mask plate in the running direction while scraping and collecting the paste supplied on the mask plate, and when the squeegee slides above the mask plate while scraping and collecting the paste, the squeegee has such a shape as to induce an agitating motion in the paste.
In this constitution, if printing at high speed, the pattern holes can be sufficiently filled with the paste material, and an excellent printing pattern is formed, and high speed printing is possible and the productivity is enhanced.